Less than
200 years ago, French American zoologist Nicolas Hentz estimated global
spider diversity to be above 2,000 species. Current estimates
(76,000-170,000)are
certainly closer to reality, but the wide range of estimates also shows
that we are still far from having a reliable estimate of spider
diversity.

For this
reason I have started several long-term projects with the aim
of
producing reasonable estimates of the actual pholcid diversity in
several
megadiverse regions: the Atlantic Forest in Brazil (ongoing project,
funded by AKG and Brazilian funding agencies), the Greater Antilles in
the Caribbean, tropical Africa (previous DFG project: HU980/9-1), and
Southeast Asia (current DFG project: HU980/11-1).
The basic idea is simple: extrapolations from species per locality,
endemism levels, and distribution patterns are combined with vegetation
data to produce a first hypothesis of overall diversity based on more
than just speculation.

Below are accumulation curves of species (y-axis) with field days
(x-axis) from the four megatransects.
Notably, none of the curves levels off; it is just the slope that
differs, depending on various factors (e.g. it is more difficult to
move
in Africa than anywhere else).

The curves
below show percentages of new
species (as of 2008) (y-axis) with field days (x-axis). After large
initial variation due to chance events, they all stabilize at about
65-85%. A rough preliminary extrapolation from these values suggests
that there are worldwide about 4000 species of Pholcidae.
More
detailed information about the
Brazilian transect is found here; details about
the expeditions are found here.